1. Field of the Invention
The invention relates to a method for preparing a carbonized nanotube composite and a method for preparing a catalyst using the carbonized nanotube composite.
2. Description of the Related Art
Carbon nanotubes (CNTs) are of great interest due to their unique mechanical strength, high electrical conductivity, and excellent chemical stability. However, they exist in the aggregated form and in parallel bundles induced by their strong van der waals and π-π interactions, making this material immiscible with most media, which is crucial to their processing. Numerous attempts have been made to develop an effective method to discretely disperse CNTs.
Strategies have been adopted to attach metal nanoparticles onto the surface of CNTs, such as functionalization of covalent-surface by oxidative treatment to generate carboxylic acid groups on the external walls of CNTs. Such surface functionalization provides a route for metal precursors to correlate with CNTs and prompts the deposition of metal on the external walls. However, approaches such as above are often considered inferior due to a lack of good control of particle size and distribution, as well as damaging the surface and reducing the unique properties such as electronic conductivity. Without surface modification, CNTs lack sufficient binding sites for anchoring precursor metal ions or metal nanoparticles, which usually leads to poor dispersion and aggregation, especially at high loading conditions.
Nitrogen doped carbon nanotubes (N-CNTs) have been studied extensively as substrate materials of catalysts for fuel cells due to their unique structure. N-doping on CNT can affect the properties such as conductivity, nanostructure and catalyst activity.
Pt-based nanoparticles are widely used as a catalyst for application in fuel cells, where they are homogeneously dispersed on various types of carbon supports. Pt supported on N-CNT can exhibit enhanced catalytic activity toward oxygen reduction reaction (ORR). Reported studies have shown that CNTs are superior to carbon blacks as catalyst supporters for proton-exchange membrane fuel cells (PEMFCs) due to their distinctive metal-support interaction, higher electronic conductivity, and good chemical stability. Compared with Pt particles trapped in the pores of a carbon black support, the Pt particles attached on the CNT surface can interact with the reactant more efficiently; but unfortunately, they agglomerate or coagulate with each other more easily. Therefore, it is of paramount importance to develop an effective synthetic method to stabilize Pt4+ and Pt(0) to prepare small and well-dispersed nanoparticles on CNTs.